I've found that not only can I not tell whether or not a mushroom has been cleaned before cooking, neither can my customers. If you make sure to shake/wipe the noticeably large dirt chunks off before cooking you'll be fine.
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FambidaSep 14 '11 at 16:22

@Fambida That seems reasonable for cultivated mushrooms, and perhaps a few wild ones, but it is hard to imagine it working for many wild mushrooms, e.g. maitake, which has lots of crevices that usually have some soil and/or bugs.
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DavidOct 13 '14 at 2:58

You're using too stiff of a brush then ... I keep three around -- a really stiff one for cleaning pots, a medium one for scrubbing root vegetables, and a soft one for mushrooms and de-silking corn. And remember -- for mushrooms, you're just lightly brushing them off, not trying to scrub them like to would to clean a potato.
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JoeJul 11 '10 at 5:03

For larger white and crimini mushrooms I typically just brush them off lightly with a dry paper towel. Wet towels tend to smear the dust across the mushroom. I dislike mushroom brushes as they just clutter up the drawers and paper towels are always available if needed.

Button-size mushrooms tend to be more likely to be dusty and are difficult to hold onto so the above method isn't very effective. For these, place them in a bowl of cool water and quickly swish them around. Then lift them out and onto some absorbent paper towels or terry towels and pat them dry. Don't drain the mushrooms in a colander as you'll just be pouring the dust back on them. Don't wash anymore than you intend to use as excessive moisture is the primary enemy of mushrooms and can make them begin to deteriorate. Excessive handling and washing can damage the surface cells which will cause discoloration.

Shiitake and Oyster mushrooms typically don't need to be cleaned in either way as they are rarely dirty.

A small brush (such as artist's brush) can be beneficial for cleaning morels since they are truly "wild" and can have bugs and dirt inside their nooks and crannies.

I didn't know that some mushrooms didn't need to be cleaned.
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hobodaveJul 18 '10 at 23:44

3

Cultivated mushrooms (white, crimini, shiitake, oyster, enoki) are grown in a medium that is typically sterilized before being inocculated with the mushroom spores. Shiitake and oyster and enoki rarely have any dust on them. Mushroom dust is probably MUCH cleaner than things we've eaten and had no idea of in the first place. White (also sometimes called "Parisian" because they were formerly grown extensively outside Paris), Crimini and Portobello (which are simply overgrown crimini mushrooms) are the ones typically needing washing if they do at all.
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Darin SehnertJul 19 '10 at 13:46

The conclusion is that you should wash the mushrooms in water.
They do not soak water from a quick rinsing.

SCENE 10

Home Office

Know what this is? This is an instrument of torture. It's called a mushroom brush. Now when you're first starting out in the restaurant
business, you spend a lot of time with one of these. And it's not a
very good time. Now why would you want to brush a mushroom? Well,
because they grow in dirt. Well, actually it's not dirt. It's compost.
But it's pasteurized compost, so it's safe. But it still doesn't taste
very good. It's got to come off. So why not just wash it off? Good
question. Allow me to read from a respected culinary tome on the
subject. Ah, mushroom ... there.

"Mushrooms are extremely porous. And because of that, they will absorb
any water or other moisture they are placed in. Because of this, they
should never be washed, only cleaned with a fine bristle brush."

Which leads us back to the instrument of torture. So is this fact or
is it fiction? Well, I for one believe there's a very, very easy way
to find out.

It is important to note that a) this experiment was done with one type of mushroom - the white button mushroom and b) only the effect on weight was measured, not the effect on taste. The OP specifically asked about the effect on taste (-1)
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DavidOct 13 '14 at 3:04

I use a soft brush (shaped like a mushroom!) and running water. Mushrooms don't absorb very much water, despite what you might think, so it's not a problem to wash them. If you're going to fry them, and are worried about splattering, they'll air dry fairly quickly after washing.

And yes, mushrooms are grown on rotting wood and composted manure. Not going to hurt you, but it's a little distasteful not to wash them!

I'm not a very sophisticated cook so I only ever use white button or Crimini mushrooms. I wash them quickly in a large bowl of water then pour them into a strainer to get rid of the water and finish by "drying" them in a salad spinner. The spinner works amazingly well to remove any water left behind.

I use a small knife to remove the small soil/dirt props. Works great. Sometimes I have some water running to clean the knife with, but a board works OK too. This way I don't need to use water or special brushes.

I like to just wet my hands with water and wipe off the dirt. That way the solvent properties of water help to clean it up more than a dry brush or towel would, and I'm not drenching it in water. I always buy them organic considering how close they are to dirt.

A great tip that I learned from a famous French chef is to wash the mushroom skin with lemon juice. He also recommended to cook it on low fire with a little water on a pane until all the initial "green liquid/subtance" comes out (you should throw that liquid away).
We did it for the preparation of a "blanquette de veau". The result was very nice.